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a fost răspuns

21+22+23+........+98+99=6x
x=?

Răspuns :

Lucian77xxl
1+2+3+...+99-(1+2+3+...+20)=(99*100)/2-(20*21)/2=99*50-10*21=4950-210=4740
AllyAllexya21
21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+55+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70+71+72+73+74+75+76+78+79+80+81+82+83+84+85+86+87+88+89+90+91+92+93+94+95+96+97+98+99=6x 
Aduni tot ce este inainte de egal : 
225+345+445+545+645+745+845+945=6x
4740=6x
X=4740:6
X= 790

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